This is a U.S. national stage of application No. PCT/JP2004/004076, filed on 24 Mar. 2004. Priority under 35 U.S.C. §119(a) and 35 U.S.C. §365(b) is claimed from Japanese Application No. 2003-083692, filed 25 Mar. 2003, the disclosure of which is also incorporated herein by reference.
1. Field of the Invention
The invention relates to a deposition system which is capable of forming a metal compound thin film by atomic layer.
2. Description of the Related Art
In recent years, intensive studies have been made on the use of high dielectric constant thin films, called high-k, as materials for constituting semiconductor devices. High dielectric constant thin films are formed by such methods as CVD (Chemical Vapor Deposition), ALD (Atomic layer deposition), and sputtering. Of these, ALD is a method for forming a thin film by cyclic supply of reactants for chemical substitution, not by thermal decomposition. This method provides a superior capability for split-level coating as compared to physical deposition methods such as sputtering, and also allows low-temperature processes. It is thus considered as a promising method for forming a high dielectric constant thin film to constitute a semiconductor device (for example, see Japanese Laid-Open Patent Applications 2001-152339, 2001-254181, and 2002-314072).
A system for conducting this ALD-based deposition appears in Japanese Laid-Open Patent Application 2001-254181. This deposition system is one for achieving the process of supplying a first source gas to a substrate placed in a deposition chamber, purging this source gas, and then supplying a second source gas thereto. Switching the source gases and the purge gas alternately at speed allows deposition through the foregoing process, whereby atomic layers can be deposited layer by layer.
Now, Japanese Laid-Open Patent Application 2002-314072 (FIG. 8) describes a deposition system which has a chamber for performing deposition processing and a chamber for performing preprocessing separately. FIG. 14 is a diagram schematically showing the structure of this ALD system. The same document describes that when the ALD system deposits Al2O3 on a silicon substrate, terminating hydrogen on the silicon surface shall be desorbed. For example, this hydrogen desorption process is performed in an atmosphere of 400° C. or above in temperature, whereas Al2O3 is deposited at around 300° C. When these processes are performed continuously in an ordinary ALD system, the sample must be once raised to 400° C. or above in temperature for the sake of the hydrogen desorption process, and then the deposition is performed after a wait until the sample temperature falls to around 300° C. Then, performing the series of operations wafer by wafer increases the number of processes of the ALD system, thereby making the cost of the semiconductor device higher.
The deposition system shown in FIG. 14 is to address this problem. The ALD system has a sample introduction chamber 13 which accommodates to-be-processed and processed samples, a reaction chamber 12 where depositing a predetermined film on a sample is carried out, and a conveyor system which conveys the samples in succession. Aside from these, the ALD system is also provided with a hydrogen desorption chamber 11 which performs the hydrogen desorption process. In the hydrogen desorption chamber 11, the hydrogen desorption process is carried out by using a heating lamp 16. This configuration allows the hydrogen desorption process and the deposition of the dielectric film, having different processing temperatures, to be performed continuously. Because of the provision of the respective chambers for performing the deposition processing and the preprocessing, it is possible to perform the processes continuously without waiting for the temperature to settle. Then, it has been concluded that the number of processes of the semiconductor device can be decreased to reduce the manufacturing cost of the semiconductor device.
Any of the deposition systems for performing such ALD-based deposition is basically configured so that a source gas and a purge gas are supplied alternately. Hereinafter, a typical ALD deposition process to be achieved by these deposition systems will be described with reference to FIG. 1. Here, the description will deal with the case of an aluminum oxide film.
Initially, a substrate is placed in the reactive chamber, and then a film material A is supplied to the surface of the substrate. Here, trimethyl aluminum (Al(CH3)3; referred to as “TMA”) is supplied (S101).
Next, the material A is exhausted from the reaction chamber by inactive gas purging (S102). Next, a reactive gas is supplied to the reaction chamber (S103). The reactive gas may be oxygen, water vapor, or the like. As a result, an oxygen atomic layer is formed on the atomic layer made of the material A. To remove resulting by-products and the reactive gas hanging in the vapor phase, inactive gas purging is then performed to exhaust the air (S104).
The foregoing steps S101 to S104 are repeated to form a high dielectric constant thin film. Subsequently, whether a predetermined thickness is reached or not is checked by a thickness measuring device which is arranged on the deposition system (S107). If it is confirmed that the predetermined thickness is reached (Yes at S107), then thermal annealing is performed for the sake of film refining processing (S108). This thermal annealing is performed after the completion of the layer formation (Japanese Laid-Open Patent Application No. 2001-152339, paragraph 0047). This completes the deposition steps.
In such a deposition process, however, impurities resulting from the materials used in the ALD have sometimes remained in the high dielectric constant thin film or induced film defects. In this respect, description will be given with reference to FIGS. 2A and 2B. FIGS. 2A and 2B are schematic diagrams showing the layer structure of a high dielectric constant thin film formed by the steps of FIG. 1. FIGS. 2A and 2B correspond to the states before and after the film refining processing by the thermal annealing shown in S108 of FIG. 1, respectively.
Before the thermal annealing, as shown in FIG. 2A, impurities are distributed throughout the high dielectric constant thin film. After the annealing, impurities are removed from the entire film. The film is also densified. Nevertheless, in the lower areas of the high dielectric constant thin film or near the substrate in particular, impurities tend to be removed insufficiently and remain intact. In addition, since metal oxides are typically prone to crystallization, the film can be partially crystallized in the annealed state of FIG. 2B. The residual impurities and the film crystallization described above may contribute to deterioration in the characteristics of the device that contains the high dielectric constant thin film. For example, when the high dielectric constant thin film is applied to the gate insulating film of a transistor, it may cause an increase in leak current, deviations in threshold characteristics, etc.
To solve these problems, it is desired to adopt a deposition method that not only supplies the source gases and the purge gas alternately but also exercises control of higher sophistication on the film quality. To achieve such a new deposition method, the deposition system itself must also be sophisticated in function.
Related Art List
JPA laid open 2001-152339
JPA laid open 2001-254181
JPA laid open 2002-314072 (FIG. 8)